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dyrodium
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Wheel casting

Looking at casting some custom wheels in the lead up to nats - done some resin casting before so familiar with the basics, just got a few questions on the finer aspects of wheeltastic makering. Laughing

Thinking of going with a 3D Printed Hub, but actually printed full density and smoothed this time... learnt my lesson. If they still suck could cast hubs using a master. The axles will be supported.

Eying this urethane for super sticky wheels - http://www.barnes.com.au/catalog/flexicast-p-2232.html

Too soft? They'll only be 60mm dia and 30mm wide so not too much load on the little gearmotors hopefully. NFI regarding demolding times so a little input would be appreciated Smile

Regarding hub design, how well does urethane stick? Will be scuffing the hubs up first but wondering if just ribs are enough or if I should go for the full aggressive design, maybe even go further and put radial holes in larger ribs? Seen some skateboard wheels designed like that.





Mold for the wheel will involve some kind of jig to center the hub, might get mega lazy and 3d print an entire mold or maybe smash one out of a UHMW block. Any pro tips for this? Laughing

Should I bother with pigment? I know a little goes a long (long) way and would rather ugly wheels than have them crumble apart!

Cheers dudes Smile
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Post Mon Sep 09, 2013 9:36 pm 
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miles&Jules
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Era polymers Hr50 i think was the stuff i was gonna try(i think Nick used that?)....but never seem to have a spare $80 to try he he.... Haven't tried that barnes stuff ..they are good cause you can buy a small bit to test.... Is this for an ant or feather? The printed mould sounds good...but the printed hub scares me after the printed motor mounts on our bots at Redfern he he..but ours weren't solid....so might work fine.

I've tested barnes soft trans silicone for a tyre rubber...way to soft...they rolled off the rims apparently....but then that stuff is made to look like soft skin in special effects.
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Post Mon Sep 09, 2013 11:40 pm 
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Knightrous
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I've previously bought urethane from SolidSolutions to make engine mounts. They have a good range from 20A to 100A with suppliers for all the pigments and casting release agents.

http://www.solidsolutions.com.au/
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Post Tue Sep 10, 2013 8:06 am 
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miles&Jules
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Hey nice link Aaron..... they look like they have some cool products.Very Happy
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Post Tue Sep 10, 2013 11:39 am 
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Nick
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I used the ERA CC50A urethane and was happy with the results. When I used an additive to reduce the hardness, the results were terrible; the wheels picked up far too much crud from the floor and the urethane tore too easily. I also tried a 65 durometer urethane but it had less traction on Jeff's old arena floor. wWith a higher traction painted floor, the harder urethane might wear better and still grip. There is also a new product RT60A that might be an all-round compromise.

Keep in mind that ALL the cold cast urethanes from every manufacturer are relatively low performance. The high temp urethanes all have vastly superior performance but demand the pro mixing systems. If we ever get access to a hot-mix urethane system, I would definitely be interested! Another thing to remember about cold-cast urethane is that it takes several days to fully cure at room temperature. I had to build a curing oven to get the urethane to cure in a reasonable time.

For the hubs, I found that the CC urethane did not stick well to plastic or aluminium, even with a bonding agent. I used a combination of deep rims and radial grooves to stop the cast treads coming off or spinning in place; I never had a tread give out, even when deeply cut. I would go with your 2nd render, but with much deeper radial cuts.

If you want to go in a group urethane buy, I could definitely be interested in re-making some of my old wheels...

Post Tue Sep 10, 2013 7:05 pm 
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dyrodium
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Cheers guys for all the valuable info!

You're spot on Nick, in the world of reaction casting the demolding times and strengths they can get now are unbelievable... Shocked There was a mixing gun on kickstarter some time ago that was designed to fit on the end of a cordless drill. Would love a tool like that!

I ended up going with the flexicast45 pretty much on availability and price - $33 for 1KG of resin ain't half bad and I wasn't in a rush to demold. Shame it's an opaque yellow, tried to colour it to orange but didn't put enough pigment in.

This is the mold I made, so it's got a base which has a rim cut into it, and a peg to centre the hub, the rim of the mold is a super thin wall 3D Print and presses into the base, with some klean clay to stop any leaks (actually they went broke haha its called something else now).

Light coat of release went on the mold, then I scuffed up the hub and put it in place.


The mix and pour was uneventful, though I need a bit of practice pouring to stop bubbles, I reckon if I get into doing this more I'll make a DIY vacuume chamber to help release the bubbles. Highly recommend the 3 cup mixing method, measure part A and B in separate cups, then combine then pour into one final cup to ensure no unmixed resin makes it to your mold.


18hrs or so later... Need better tolerances on the hub centring peg to keep it locked down on the bottom a bit better, it was a bit too loose for this first test.


Wheel freed from mold jail, I split the outer ring in half to remove it, but am now thinking I could actually just design it with a split, plug that with klean clay during the cast and it'd easily just flex away - reuseable woot.


Emegerd wheel :3 Shame I've given up on coming with a new featherweight for this years nats >_> but if anything, I reckon this casting method has a huge potential for ants... going to try a set of ant wheels next. Need to do a bit of testing to see if the hardness of the rubber is suitable for wheels first.

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Post Fri Sep 13, 2013 9:59 am 
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Nick
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Great work! I like the simple mould, its much easier than the ones I made. Would it help if you used a bolt right thru the wheel hub rather than just that stubby pin? I bolted my hubs into the bottom plate of the moulds and it worked really well. The only reason that I haven't made any more urethane wheels is that Colson wheels are cheap and good enough.

Post Fri Sep 13, 2013 10:11 am 
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miles&Jules
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Looks genius Angus cant wait to see how it goes ....one way of making an awesomely cheep degasser to get rid of those bubbles....is

-get a old source pan (20cm wide is good).....

-get a piece of perspex to cover the top of it (might need two layers)

-get a piece of rubber sheet same size as the perspex.

-tap a pneumatic air hose in the side of the source pan

-run the air hose to the intake of an air compressor

-cut a hole in the sheet of rubber so you can see through the perspex into the "tank"

-then mix up ya urethane put it in the tank

-turn on the compressor and the mixture will start bubbling as al the bubbles get sucked out.

home made degasser....for under $20
Very Happy
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Last edited by miles&Jules on Wed Oct 23, 2013 10:14 am; edited 1 time in total

Post Fri Sep 13, 2013 10:35 am 
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dyrodium
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Cheers guys,

@ Nick the difference is you did it properly! Laughing The hubs had a D so that's why I went with a peg, but looking at it I could fit an M6 through it as well as the peg, great idea!

@ Miles yep absolutely going to be making one of those little contraptions! I only have shop vac but have seen people use those instead of compressors. Does yours have a valve to lock in the vacuum or have you found it isn't needed? Do you ever degass once the material is poured into the mold or always while it's still in the mixing cup?

Smile
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Post Fri Sep 13, 2013 11:17 am 
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miles&Jules
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Yeah i have got pne of those valves-you need it or you will never get the lid off after you have degassed it-usually its the mixing that creates the bubbles so degas it in the mixing container -then pour it in a long thin stream into the mold -you get less bubbles that way
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Post Fri Sep 13, 2013 5:57 pm 
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dyrodium
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Hehe when in doubt ask the pro's. Very Happy Another dumb question, what valve should I source? Totally noob at anything pneumatic... Rolling Eyes
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Post Fri Sep 13, 2013 6:35 pm 
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miles&Jules
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Any gas type one will do-i got a yellow leaver action one from bunnings which is fine-pros would have the budget to buy a real $3k degasser he he
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Post Fri Sep 13, 2013 7:04 pm 
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Jaemus
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Very nice Angus!

Miles/jukes I think I might have some questions for you guys when I start a headlight lens reproduction project I have in mind Smile
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Post Sat Sep 14, 2013 2:00 pm 
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Nick
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How much of a vacuum do you need to de-gas and how long does it take? When I was making urethane wheels, I used a giant syringe to suck up the plastic and then inject it into the moulds, which really cut down waste and mess. If the plastic was sucked up and then I blocked the syringe nozzle, would pulling back the plunger further be enough to de-gas the plastic?

I like your DIY saucepan de-gasser so next time I could easily build one of those if the idea above won't work.

Post Sat Sep 14, 2013 2:27 pm 
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miles&Jules
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will try and help Jeamus

@Nick only takes a 10 seconds or so...you just look through the perspex and see the mixture start bubbling........it even makes water bubble......never tried it on a vacuum cleaner but i suspect it wont be at brutal as the air compressor intake.....I've used a real $3k degasser at movie world and the bunnings $100 air compressor trick works just as good. Very Happy
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Post Sat Sep 14, 2013 5:16 pm 
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